Speed sensing air tool shutoff

ABSTRACT

A shutoff for a pneumatic tool such as a nut runner is disclosed. The shutoff, effective to terminate air supply to the air motor under stall loading conditions of the tool, employs a centrifugally operated main air valve and a starting bypass valve. In operation of the tool, air is initially supplied to the air motor through the bypass valve. When the motor reaches a predetermined speed level, the centrifugally operated main valve is opened, and the bypass valve is closed thereafter. Under loading, approaching stall, the motor slows to a speed low enough to allow the main valve to close under the influence of a spring. Because the shutoff occurs before the stall condition is attained, stall jerking is substantially eliminated.

United States Patent 11 1 Boyd Sept. 9, 1975 [54] SPEED SENSING AIR TOOLSHU'IQFF 3,697,189 10/1972 Tibbott 415/25 3,752,241 8 1973 Be t 415 503[75] Inventor: Horace Edward Boyd, Euclid, Ohio 3 785 442 1, Arrtsberget a1. H 41/5/36 73 Assignee: Cooper lndusu-ies, Inc. Houston, 3,791,4582/1974 Wallace 137/58 Tex.

Primary ExaminerC. J. Husar 1 1 Filed: 19, 1974 Attorney, Agent, orFirmOwen & Owen Co. [21] Appl. No.: 498,619

[57] ABSTRACT A shutofi' for a pneumatic tool such as a nut runner is[52] 415/25 fg disclosed. The shutoff, effective to terminate air sup- 2I ply to the air motor under stall loading conditions of [51] Int. Cl.F0 5122/00 the tool, employs a centrifugal), Operated main air [58] f gZ. valve and a starting bypass valve. In operation of the I I l tool,air is initially supplied to the air motor through the bypass valve.When the motor reaches a predeter- [56] Reierences Clted mined speedlevel, the centrifugally operated main UNITED STATES PATENTS valve isopened, and the bypass valve is closed thereaf 2,246,910 6/1941 Amtsberg91/59 ter. Under loading, approaching stall, the motor slows 2,768,54610/1956 Amtsberg 415/503 to a speed low enough to allow the main valveto close 2925-089 2/1960 Conkli" 415/503 under the influence of aspring. Because the shutoff al f r occurs before the stall condition isattained, stall jerkltc ouse n v 3,384,343 5/1968 Bangcrtcr 415/503 mgsubsmm'auy el'mmated 3,608,647 9/1971 Borries 91/59 11 Claims, 9 DrawingFigures 5 r \r w 1 e Z I 42 9 11 f /2 l 2s /9 /3 l q 6/ 2 /6 l 24' L 1L1 l 7 I 1'- L g I; l 7 l 0 7 3/26 27 I4; 5, L 3 r PATENTED 91975 SHUT 1OF 3 PATENTEDSEP 9:975 3,904,305

SHEET 2 BF 3 SPEED SENSING AIR TOOL SHUTOFF BACKGROUND OF THE INVENTIONThe invention relates to pneumatic rotary tools, and more particularlyto a pre-stall air shutoff for such tools which is dependent upon aspeed responsive device to sense the approaching stall and shut off thetool.

Most prior art rotary tools using a vane-type air motor have used apressure sensing valve to automatically shut off the tool as the torqueresistance encountered caused a build up of back pressure from the airmotor to a predetermined value. Examples of such tools are disclosed inU.S. Pat. Nos. 3,373,824 and 3,608,647. This pressure sensitive system,while satisfactory in many applications, has disadvantages in that it issensitive to line pressure variations. A pressure surge in the line, forexample, can prematurely stop the tool. Similarly, sudden opening of thethrottle valve can sometimes cause a surge sufficient to activate theshutoff. The most serious effect of pressure sensitivity in such tools,however, occurs when line pressure is too low to activate the shutoff.This condition can occur when there is overdraw on the air line, forexample. With a high-torque tool, failure of the shutoff to activate canresult in an unexpected and dangerous stall jerk on the operator.Another problem with pressure responsive shutoffs is their sensitivityto air line lubrication and to contaminants carried by the supply air.Hose residue, for example, can interfere with the valving of such toolsto the extent that torque output is affected.

Other prior art tools have used mechanical means such as clutches orratchet-type devices to control the effective output torque upon afastener or joint; these devices are usually complex and subject to wearand thus continuous maintenance costs. They also will produce a stalljerk if a pressure drop of sufficient magnitude to reduce motor torquebelow the clutch setting is encountered.

A tool of the type to which this invention relates is shown in WallaceU.S. Pat. No. 3,79l,458. Designed to relieve the stall loading jerk onan operator during tightening of a fastener, the tool employs a speedsensitive air shutoff which terminates air supply to the air motor at aspeed just above stall. The tool disclosed in that patent utilizes aslidable spool-type valve which is spring-biased toward its openposition. A pressure chamber at the lower end of the slidable valvemember receives pressurized air as long as the tools throttle valve isopen. However, once the air motor of the tool has built up a degree ofspeed, an exhaust outlet from the pressure chamber prevents the chamberfrom fully pressurizing to move the valve to the closed position. Arotatable, centrifugally responsive ball and seat valve is employed tokeep the exhaust outlet open during normal operation of the tool but toclose it during low speed associated with a stall, allowing the chamberto fully pressurize and close off the air supply to the motor. Theprimary disadvantages of this tool are construction and maintenancecost. The tool involves rather complex structure including a rotationalair coupling which is subject to a great deal of wear, resulting inerratic tool operation.

SUMMARY OF THE INVENTION The present invention provides a speedresponsive air tool shutoff which utilizes a centrifugally operated mainoperating air valve somewhat similar to a conventional governor tocontrol the point of shutoff of the tool. A separate starting or bypassair valve is included, in addition to the usual throttle valve. When thethrottle valve is closed, the main valve remains closed under theinfluence of a compression spring and the bypass valve remains openunder the influence of a second compression spring. When the throttlevalve is opened, a limited supply of pressurized air is admitted to themotor through the bypass valve, permitting the motor to rapidly build upinitial speed during rundown of the nut or bolt. As a predeterminedminimum speed is reached, the main operating air valve is opened bycentrifugal weights, admitting air to the motor at a much greater flowrate. Shortly after the main valve opens, the bypass valve is closed bythe pressurization of an expansible chamber. The pressure chamber ispositioned at one end of a slidable member, the position of whichdetermines whether the bypass valve is open or closed. Pressurized airfrom the throttle valve is gradually admitted to the chamber through anorifice. The size of the orifice in relation to the expansion volume issuch that closure of the bypass valve is delayed until after the mainvalve is opened.

As the joint begins to tighten and the tool encounters increasedresistance, the speed of the air motor begins to decrease. At apredetermined low motor speed representative of the desired appliedtorque, the centrifugal valve opening means is overcome by the mainvalve compression spring, and the main valve begins to close. Theclosure of the valve is accelerated when it reaches a certain point atwhich pressurized air from the throttle valve is admitted to anexpansible chamber in the main valve which expands to quickly snap closethe main valve, thus shutting off all air to the motor and stopping thetool shortly thereafter so that an accurate torque has been applied tothe joint.

As long as the throttle valve is held open, both the main valve and thebypass valve remain closed. Upon closure of the throttle valve, thepressurized condition of the bypass valves expansible chamber isdissipated to the atmosphere through the orifice and the throttle valve,allowing the bypass valve to reopen so that the tool may again bestarted by opening of the throttle valve.

A second embodiment of the invention employs a different type startingbypass valve which closes in direct response to the opening of the mainvalve rather than after a time delay depending on an orifice. At one endof a slidable member of the bypass valve is an expansible chambersimilar to that of the first embodiment, but the chamber receivespressurized air from a cavity adjacent and downstream of the main valverather than from a point upstream of the main valve. Bypass air is thusable to reach the chamber initially but does not exert enough pressurein the chamber to close the bypass valve. Only when the main valve opensis there sufficient pressure available to expand the chamber and closethe bypass valve. As the bypass valve closes, it seals ofi' a port whichsupplies its chamber with high pressure air, but simultaneously opens aninterlock port which delivers high pressure air directly from thethrottle valve. Without this interlock, the bypass valve would reopen,allowing the tool to continue running after the main valve has closed.

The speed sensitive air shutoff of the present invention does not relyupon the sensing of air back pressure for its operation, and thusovercomes the disadvantages of the pressure sensing tools discussedabove. In particular, the present shutoff activates at a given low motorspeed regardless of variations in line pressure, eliminating danger ofinjury to the operator. Another advantage of the speed sensing featureis the ability to regulate output torque simply be varying linepressure. The tool is also relatively simple in construction andoperation, requiring little maintenance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of aportion of a rotary air tool including an air shutoff according to thepresent invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a view similar to FIG. 1 but with the main valve of theshutoff in the open position;

FIG. 4 is a view similar to FIG. 3 but with the bypass valve of theshutoff in the closed position;

FIG. 5 is another similar view showing both the main and bypass valvesin the closed position;

FIG. 6 is a sectional view taken along the line 66 of FIG. 5;

FIG. 7 is a sectional view of another embodiment of the invention;

FIG. 8 is a sectional view similar to FIG. 7 but with the shutoff rnainvalve open and the bypass valve closed; and

FIG. 9 is another similar view showing both the main and bypass valvesin the closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I of the drawings shows insection a portion of an air tool 10 such as an angle nut runner. Thetool 10 includes an air motor 11, a throttle valve 12 behind which is achamber 13 communicating through a pressure regulator 15 with a sourceof pressurized air (not shown), and a speed sensing air shutofi' 14between the throttle valve 12 and the motor 11. The shutofi 14 isadapted to terminate the flow of pressurized air from the throttle valve12 to the air motor 11 when the motor I l slows to a given speedapproaching stall while torquing a fastener, and to keep the air supplyshut off until the throttle valve 12 is again closed.

As FIG. 2 indicates, the throttle valve 12 includes a depressing lever16 on the exterior of the tool, a valve stem 17, a seat 18, a closingmember 19, and a compression spring 21 biasing the valve 12 toward itsclosed position. The structure of the throttle valve 12 is typical ofmany air tools and is not considered to be a part of this invention.

Downstream of the throttle valve 12, as FIGS. 1 through 5 indicate, theshutoff means 14 includes a main operating valve 22 which is open duringtorquing of the work and during most of the rundown of the work. Thevalve 22 includes a valve closing sleeve 23 which is slidable upon arotor shaft extension 24 driven by the motor 11. The sleeve 23 is notkeyed into the shaft extension 24 for rotation therewith; it may rotatewith or rotationally slip upon the shaft extension 24. The upstream endof the valve closing sleeve 23 is positioned to come into contact with aflange 26 of a stationary sleeve 27 affixed to the body of the tool 10.In this position of the slidable valve sleeve 23, the space between theupstream end of the rotor shaft extension 24 and the stationary flange26 is closed, thereby preventing the passage of air therethrough.

A compression spring 28 biases the valve sleeve 23 toward its closedposition. In addition, an oblique bore 29 is provided through theupstream end of the rotor shaft extension 24 for accelerating theclosure of the valve sleeve 23 once it has progressed beyond a certainpoint. That point is defined by the uncovering of the downstream end ofthe bore 29 by the valve closing sleeve 23. This enables pressurized airfrom the throttle valve 12 to enter an expansible chamber 31 definedbetween the rotor shaft extension 24 and the surrounding valve closingsleeve 23.

The valve 22 is opened by centrifugal weights 32 pivotally connected toa rotating yoke 33. As shown in FIGS. 1 and 3, the weights 32 areadapted to urge the valve sleeve 23 against the spring bias to open thevalve 22 upon the attainment of the predetermined motor speed level. AsFIG. 6 indicates, six such weights may be provided on the yoke 33. Itshould be noted here that, contrary to the usual arrangement of acentrifugal weight governor, the valve 22 here is opened by increasedspeed and closed by decreased speed.

In order to initially supply pressurized air to the motor 11 before thevalve 22 has opened, a bypass assembly 34 is provided. As shown in FIG.I, the valve assembly 34 in the open position provides air communicationfrom the throttle valve to the motor 11 through a duct 36 in a slidablespool 37 which resides within a bore 40. The upstream end of the duct 36is always open to a chamber 38 communicating with the throttle valve 12,and during the open position of the bypass, the downstream end of theduct 36 communicates through an annular chamber 39 with a bore 41 in thebody of the tool 10. As the figures indicate, the bore 41 is always opento the air motor II. The valve spool 37 is biased downwardly toward itsopen position by a compression spring 42 positioned in a chamber 43which is open to the atmosphere through a breather port 44 in the bodyof the tool 10. A low friction O-ring 47 is provided to seal the valveassembly 34 against leakage of pressurized air through the opening 44.

The closing of the valve 34 is accomplished by the pressurization of anexpansible chamber 48 defined be tween the lower end of the spool 37 anda threaded plug 53 which forms a boundary of the bore 40. A low frictionO-ring 50 seals the chamber 48 from air leakage. To provide the requiredrate of pressurization, a small orifice 51 through the valve spool 37admits pressurized air at a measured rate from the chamber 38 into theexpansible chamber 48. The size of the orifice 51 is such that thechamber 48 receives sufficient air to pressurize and expand, thusraising the spool 37 and closing the valve 34, after the main operatingvalve 22 has opened in response to the attainment of the proper motorspeed level. The closed position of the bypass valve assembly 34 isshown in FIGS. 4 and S.

In operation of the speed sensitive shutoff 14 of the rotary air tool10, the line air pressure or flow regulator 15 is first adjusted to asetting corresponding to the desired output torque. Pressurized air isthen admitted through the throttle valve 12 by the operator's depressionof the lever 16. Air is thus supplied to the motor 11 in limitedquantity through the ducts 36 and 4] of the bypass assembly 34. Thisinitial bypass air is sufi'icient to start the motor and quickly bringit to about 5000 rpm or more. At this time, the output spindle (notshown) of the tool is engaged in the running down of a fastener. Duringthis phase, the output spindle torque of the tool, though lower thanthat of the next phase, is sufficient to run down even a prevailingtorque" fastener. The position of the shutoff apparatus 14 during thisphase of operation is shown in FIG. 1.

When the motor 11 reaches a predetermined speed which may be in therange of l500-2000 rpm, the pivoted weights 32 on the rotating yoke 33swing out, urging the valve sleeve 23 in a downstream direction againstthe bias spring 28 as shown in FIG. 3 and opening the main operatingvalve 22. The weights 32 preferably swing through an angle of about 36,overcoming the pressure of the spring 28 and any residual air pressurebias in the chamber 31, as well as friction. The bypass valve assembly34 remains in the open position while the main valve 22 is opening andfor a short period thereafter, the length of which is determined by therate of pressure buildup in the chamber 48, which in turn depends uponthe sizing of the small orifice 5].

The next phase of operation of the air tool is shown in FIG. 4. Theexpansible chamber 48 at the base of the slidable bypass valve spool 37receives pressurized air through the orifice 51 as long as the throttlevalve 12 is open. When the pressure in the chamber 48 is sufficient toovercome friction and the compression spring 42, the chamber 48 expands,sliding the valve spool 37 upward against the pressure of the spring 42and the friction of the Orings 47 and S0 to shut off the supply ofbypass air through the duct 36. At this point, the tool 10 is stillengaged in the rundown of the fastener, requiring relatively littletorque.

With the main operating valve 22 open and the bypass valve assembly 34closed as shown in FIG. 4, the tool 10 completes the rundown and beginsthe torquing of the fastener. The two valves remain in this positionuntil the motor ll, during torquing of the fastener, has slowed to nearstall, i.e., in the range of l00l000 rpm. At this speed, representativeof the desired final torque on the fastener, the valve sleeve 23 of themain valve assembly 22 begins to slide toward the closed position, thepressure of the return spring 28 being greater than the centrifugaleffect of the weights 32.

As the valve sleeve 23 closes the valve 22, air pressure upstream of thevalve 22 increases and downstream decreases. When the closure of thevalve sleeve 23 has proceeded to such a point that the downstream end ofthe oblique air passageway 29 is uncovered, the expansible chamber aboutthe spring 28 is immediately pressurized by high pressure air and thesleeve 23 com- I pletes its closure with a snap action. Both the mainvalve 22 and the bypass valve 34 are now closed, as shown in FIG. 5. Theair supply to the motor 11 is thus totally shut off and the motor 11stops.

Although the operator of the tool 10 may hold the throttle valve 12 openafter shutoff of the tool, air flow to the motor 11 will not be resumed.As FIG. 5 indicates, pressurized air from the open throttle valvecontinues to be available to the chamber 48 through the orifice 51,thereby maintaining the closed position of the bypass valve assembly 34.When the throttle valve 12 is ultimately closed by the operator, highpressure air no longer reaches the chamber 48 and it is quicklydepressurized by bleeding of air from the chamber 48 to the atmospherevia the orifice 51, the air chamber 38 and a flat 54 on the valve stem17 of the closed throttle valve 12. The spring 42 thus returns the valvespool 37 to its original position and the bypass valve is reopened forthe next usage of the tool 10.

FIGS. 7, 8 and 9 illustrate another form of the invention. As in theabove described embodiment, a rotary air tool 55 of this embodimentincludes a throttle valve 56, a main air valve 57 and a bypass valveassembly 58. The main valve 57 is identical in structure and operationto the valve 28 of the first embodiment. The bypass valve assembly 58 issimilar to the bypass 34 of the above embodiment in that it includes aslidable valve spool 60 which defines an expansible chamber 59 with aplug member 61 below and it is biased downward toward its open positionby a compression spring 62. In the open position, pressurized air fromthe throttle valve 56 passes through a chamber 38' and a channel 63appearing behind the valve spool 60, through an annular passage 64 inthe spool 60 and through a duct 66 from which it travels to an air motor67. As is true in the above embodiment, air from the throttle valve 56can pass with little restriction around the valve spool 60 en route tothe main air valve 57 regardless of the position of the valve spool 60.

The difierence between the bypass valve assembly 58 and the above bypass34 is the manner in which the expansible chamber 59 is pressurized toslide the valve spool 60 upward to its closed position. The chamber 59receives sufficient pressure to close the bypass valve in directresponse to the opening of the main air valve 57. As FIG. 7 indicates, aport 68 provides communication between the downstream side of the mainand bypass valve assemblies 57 and 58 and an annular chamber 69 andcrossport 70 in the spool 60 leading to the expansible chamber 59. Thus,in the open bypass position of FIG. 7, pressurized air from the throttlevalve passing through the bypass assembly 58 is in communication withthe expansible chamber 59. However, because of restrictions defined bythe channel 63, the annular passage 64 and the duct 66, bypass airreaching the duct 68 for entry into the chamber 59 is undersubstantially lower pressure than the air immediately downstream of thethrottle valve 56. The pressure thus developed in the chamber 59 is notsufficient to move the valve spool 60 against the pressure of thecompression spring 62 and a degree of air pressure within a chamber 72defined above the valve spool 60. Some air pressure develops in thechamber 72 whenever the throttle valve 56 is open by leakage from theannular passage 64 of the valve spool around the upper portion of thevalve spool, which is not sealed. An orifice 73 leading from the chamber72 to the atmosphere limits the pressurization of the chamber 72.

When the main air valve 57 is opened by the necessary motor speed, airpasses to the downstream side of the valves 57 and 58 and to the motor67 at much greater pressure, since few restrictions are encountered.This enables high pressure air to pass through the port 68, the annularchamber 69 and the crossports 70 into the expansible chamber 59, whichthen expands to move the valve spool 60 upward toward the closed bypassposition seen in FIG. 8. As the spool 60 moves upward, the annularchamber 69 is cut off from the port 68. However, before this occurs, thechamber 69 is put in communication with an interlock channel 74, appearing behind the valve spool 60, which receives compressed airdirectly from the throttle valve 56. There is thus a continuity of highpressure air flow into the chamber 59, and the valve spool 60 rises tothe closed position of FIG. 8 and is held there by air from theinterlock channel 74. The pressure within the air chamber 59 is nowgreater than the combined effects of the compression spring 62 and theair pressure within the upper chamber 72. The tool 55 operates in theposition of FIG. 8 until the shutoff speed is attained as the motorslows during tightening of a fastener.

FIG. 9 indicates the positions of the main and bypass valve assemblies57 and 58 after the air motor 67 has slowed to a speed low enough toallow the main valve 57 to close. As long as the throttle valve 56 isheld open, the expansible chamber 59 continues to receive pressurizedair and thus remains in its closed position. When the throttle valve 66is closed, the pressure in the chamber 59 dissipates through normalleakage. Some air passes through the port 68, seeping out through themotor 67, while some air leaks upward through the channel 63, around theupper portion of the valve spool and out of the orifice 73. The valvespool is thus quickly returned to the open bypass position by thecompression spring 62, and the tool is again ready for operation in theposition of FIG. 7.

The above described preferred embodiments provide speed responsive airtool shutoffs which are simple and effective in operation, requiringlittle maintenance. Various other embodiments and alterations to thesepreferred embodiments will be apparent to those skilled in the art andmay be made without departing from the spirit and scope of the followingclaims.

I claim:

1. A speed sensitive shutoff for a rotary air tool having an air motoroperable by a throttle valve with an air passage therebetween,

a main air valve in said air passage between the air motor and thethrottle valve including means biasing the valve toward its closedposition to close off said air passage,

means for opening said main valve in response to the attainment of apredetermined upper motor speed level and for closing said main valve inresponse to the attainment of a predetermined lower motor speed level,

a normally open starting valve positioned in parallel relationship withsaid main air valve and effective to bypass air around said main airvalve to said motor, and

means for closing and maintaining closure of said starting valve duringoperation of the tool after said main valve has opened and until thethrottle valve is closed,

whereby, while the throttle valve of the tool is open, the air supply tothe air motor continues until the motor speed slows to saidpredetermined lower motor speed level, then ceases until the throttlevalve is closed and reopened.

2. The speed sensitive shutoff of claim 1 wherein said main valveopening means and closing means comprise weights mounted adjacent to thevalve for rotation with the air motor, said weights being effective, inresponse to centrifugal force induced by said predetermined upper motorspeed level, to open said main valve against said biasing means, andeffective, in response to a lower level of centrifugal forcecorresponding to said predetermined lower motor speed level, to allowsaid biasing means to close said main valve,

3. The speed sensitive shutoff of claim 1 wherein said main valveopening means and closing means include centrifugal weights mounted forrotation with the air motor and for outward displacement duringoperation of the motor above said predetermined lower motor speed level,said main valve being opened in response to outward displacement of saidweights.

4. The speed sensitive shutoff of claim 1 wherein said main air valveincludes, in addition to said biasing means, means for accelerating therate of valve closure after it has proceeded beyond a predeterminedpoint.

5. The speed sensitive shutoff of claim 4 wherein said acceleratingmeans comprises a rotating shaft and an axially slidable sleeve mountedcircumjacent thereon for rotation therewith, said sleeve and shaftdefining an expansible chamber which upon expansion moves the main valvetoward closure, and means placing the chamber in communication withpressurized air from the throttle valve after main valve closure hasproceeded beyond said predetermined point.

6. The speed sensitive shutofi of claim I wherein said starting valveincludes a slidable member within a bore of the tool, said memberdefining a bypass air passageway closeable in response to slidingmovement of the member in one direction, and means urging said member inthe opposite direction, and said starting valve closing means comprisesan expansible chamber defined by said member and said bore, saidexpansible chamber including means establishing communication withpressurized air when the throttle valve is open and being effective, inresponse to an accumulation of pressurized air therein, to move saidslidable member in said one direction to close said starting valve.

7. The speed sensitive shutofi' of claim 6 wherein said aircommunication means comprises an orifice extending from said chamberthrough said member into the path of airflow from the throttle valve,said orifice being of a predetermined size adapted to permit pressureaccumulation in the chamber sufficient for starting valve closure aftera time period sufficient to permit said main valve to open.

8. The speed sensitive shutoff of claim 1 wherein said starting valveincludes a slidable member within a bore of the tool, said memberdefining a bypass air passageway closeable in response to slidingmovement of the member in one direction, and means urging said member inthe opposite direction, and said starting valve closing means comprisesan expansible chamber defined by said member and said bore, saidexpansible chamber including means establishing communication with highpressure air from downstream of the throttle valve in response to theopening of said main air valve and being effective, in response to anaccumulation of pressurized air therein, to move said slidable member insaid one direction to close said starting valve.

9. The speed sensitive shutoff of claim 8 wherein said air communicationmeans comprises a duct extending from downstream of said main air valveto a position adjacent the slidable member, passageway means in saidmember connecting said duct with the expansible chamber, said duct beingin communication with the chamber while the bypass valve is open andduring an initial portion of the travel of the slidable member towardthe closed position, and means adjacent and downstream of the throttlevalve for establishing communication between the chamber and-highpressure air from the throttle valve during the remainder of the travelof the slidable member.

10. A speed responsive air shutoff for a pneumatic rotary tool having anair motor operable by a throttle valve, comprising a main air valvebetween the motor and the throttle valve, including means biasing thevalve toward closed position and centrifugal means for opening the valveabove a predetermined upper motor speed and for allowing the valve toclose below a predetermined lower motor speed; and bypass means forinitially admitting pressurized air from the throttle valve to the airmotor until after said main air valve has been opened.

11. A speed responsive shutoff control for a rotary fluid motorcomprising, in combination, a main fluid passage connecting a source offluid under pressure to said motor, a main shutoff valve upstream ofsaid motor, said main valve including a centrifugal governor devicedriven by said motor and operably positioned to open said main valve asmotor speed increases, said governor device being biased to open saidmain valve when said motor speed reaches a predetermined minimum, abypass valve positioned in said fluid passage in parallel relation withsaid main valve such that said bypass valve, when open, will directfluid around said closed main valve to said motor, and means formaintaining said bypass valve in its open position for only apredetermined time until said main valve is opened by said governordevice when said motor speed reaches said predetermined minimum whereby,after said motor has reached said predetermined speed to open said mainvalve and said bypass valve has closed, a subsequent drop in motor speedto a low speed below said predetermined minimum will close said mainvalve, thereby shutting off all fluid supply to said motor.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3 ,904305 Dated September 9 1975 Inventor(s) Horace Edward Boyd It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Errors due to Patent Office:

Column 1, line ll, "caused" should be -causes.

Column 3, line 7, "be" should be -by-.

Column 6, line 8, "28" should be 22--.

Column 7, line 19, delete "of".

Error due to applicant:

Signed and Scalcd this ninth Day of Decemberl975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Office Commissioner ufParenrsand Trademarks

1. A speed sensitive shutoff for a rotary air tool having an air motoroperable by a throttle valve with an air passage therebetween, a mainair valve in said air passage between the air motor and the throttlevalve including means biasing the valve toward its closed position toclose off said air passage, means for opening said main valve inresponse to the attainment of a predetermined upper motor speed leveland for closing said main valve in response to the attainment of apredetermined lower motor speed level, a normally open starting valvepositioned in parallel relationship with said main air valve andeffective to bypass air around said main air valve to said motor, andmeans for closing and maintaining closure of said starting valve duringoperation of the tool after said main valve has opened and until thethrottle valve is closed, whereby, while the throttle valve of the toolis open, the air supply to the air motor continues until the motor speedslows to said predetermined lower motor speed level, then ceases untilthe throttle valve is closed and reopened.
 2. The speed sensitiveshutoff of claim 1 wherein said main valve opening means and closingmeans comprise weights mounted adjacent to the valve for rotation withthe air motor, said weights being effective, in response to centrifugalforce induced by said predetermined upper motor speed level, to opensaid main valve against said biasing means, and effective, in responseto a lower level of centrifugal force corresponding to saidpredetermined lower motor speed level, to allow said biasing means toclose said main valve.
 3. The speed sensitive shutoff of claim 1 whereinsaid main valve opening means and closing means include centrifugalweights mounted for rotation with the air motor and for outwarddisplacement during operation of the motor above said predeterminedlower motor speed level, said main valve being opened in response tooutward displacement of said weights.
 4. The speed sensitive shutoff ofclaim 1 wherein said main air valve includes, in addition to saidbiasing means, means for accelerating the rate of valve closure after ithas proceeded beyond a predetermined point.
 5. The speed sensitiveshutoff of claim 4 wherein said accelerating means comprises a rotatingshaft and an axially slidable sleeve mounted circumjacent thereon forrotation therewith, said sleeve and shaft defining an expansible chamberwhich upon expansion moves the main valve toward closure, and meansplacing the chamber in communication with pressurized air from thethrottle valve after main valve closure has proceeded beyond saidpredetermined point.
 6. The speed sensitive shutoff of claim 1 whereinsaid starting valve includes a slidable member within a bore of thetool, said member defining a bypass air passageway closeable in responseto sliding movement of the member in one direction, and means urgingsaid member in the opposite direction, and said starting valve closingmeans comprises an expansible chamber defined by said member and saidbore, said expansible chamber including means establishing communicationwith pressurized air when the throttle valve is open and beingeffective, in response to an accumulation of pressurized air therein, tomove said slidable member in said one direction to close said startingvalve.
 7. The speed sensitive shutoff of claim 6 wherein said aircommunication means comprises an orifice extending from said chamberthrough said member into the path of airflow from the throttle valve,said orifice being of a predetermined size adapted to permit pressureaccumulation in the chamber sufficient for starting valve closure aftera time period sufficient to permit said main valve to open.
 8. The speedsensitive shutoff of claim 1 wherein said starting valve includes aslidable member within a bore of the tool, said member defining a bypassair passageway closeable in response to sliding movement of the memberin one direction, aNd means urging said member in the oppositedirection, and said starting valve closing means comprises an expansiblechamber defined by said member and said bore, said expansible chamberincluding means establishing communication with high pressure air fromdownstream of the throttle valve in response to the opening of said mainair valve and being effective, in response to an accumulation ofpressurized air therein, to move said slidable member in said onedirection to close said starting valve.
 9. The speed sensitive shutoffof claim 8 wherein said air communication means comprises a ductextending from downstream of said main air valve to a position adjacentthe slidable member, passageway means in said member connecting saidduct with the expansible chamber, said duct being in communication withthe chamber while the bypass valve is open and during an initial portionof the travel of the slidable member toward the closed position, andmeans adjacent and downstream of the throttle valve for establishingcommunication between the chamber and high pressure air from thethrottle valve during the remainder of the travel of the slidablemember.
 10. A speed responsive air shutoff for a pneumatic rotary toolhaving an air motor operable by a throttle valve, comprising a main airvalve between the motor and the throttle valve, including means biasingthe valve toward closed position and centrifugal means for opening thevalve above a predetermined upper motor speed and for allowing the valveto close below a predetermined lower motor speed; and bypass means forinitially admitting pressurized air from the throttle valve to the airmotor until after said main air valve has been opened.
 11. A speedresponsive shutoff control for a rotary fluid motor comprising, incombination, a main fluid passage connecting a source of fluid underpressure to said motor, a main shutoff valve upstream of said motor,said main valve including a centrifugal governor device driven by saidmotor and operably positioned to open said main valve as motor speedincreases, said governor device being biased to open said main valvewhen said motor speed reaches a predetermined minimum, a bypass valvepositioned in said fluid passage in parallel relation with said mainvalve such that said bypass valve, when open, will direct fluid aroundsaid closed main valve to said motor, and means for maintaining saidbypass valve in its open position for only a predetermined time untilsaid main valve is opened by said governor device when said motor speedreaches said predetermined minimum whereby, after said motor has reachedsaid predetermined speed to open said main valve and said bypass valvehas closed, a subsequent drop in motor speed to a low speed below saidpredetermined minimum will close said main valve, thereby shutting offall fluid supply to said motor.